Generation/ Low Resistance Grounding/ Distribution System
Generation/ Low Resistance Grounding/ Distribution System
(OP)
Gentlemen,
I have a plant that is serviced by a 5KV generation and distribution system. All of the loads on this system are three phase loads. If all of the generators are low resistance grounded, do I need to run a ground wire along with the phase wires from the 5KV switchgear to each of the 5KV loads (pad mounted gear, transformers, etc.) All of the loads in question will be grounded via "local" ground rods & loops.
If I do not run a ground wire with the phase conductors, is the earth an allowable return path for returning a phase to ground fault to the generator source?
I have looked in the National Electrical Safety Handbook (NESC), IEEE Std. 142, NEC and Soares Book on Grounding to shed some light or guidance, but have come away with very little.
Any guidance on this subject would be greatly appreciated.
I have a plant that is serviced by a 5KV generation and distribution system. All of the loads on this system are three phase loads. If all of the generators are low resistance grounded, do I need to run a ground wire along with the phase wires from the 5KV switchgear to each of the 5KV loads (pad mounted gear, transformers, etc.) All of the loads in question will be grounded via "local" ground rods & loops.
If I do not run a ground wire with the phase conductors, is the earth an allowable return path for returning a phase to ground fault to the generator source?
I have looked in the National Electrical Safety Handbook (NESC), IEEE Std. 142, NEC and Soares Book on Grounding to shed some light or guidance, but have come away with very little.
Any guidance on this subject would be greatly appreciated.






RE: Generation/ Low Resistance Grounding/ Distribution System
A somewhat related reference is ANSI/IEEE C62.92.4-1991 …Neutral Grounding in Electrical Utility Systems, Part IV—Distribution. Although §2 deals primarily in system grounding, the multigrounded system is successfully used in many areas on the North American continent.
In cases where earth return is relied upon to operate medium-voltage overcurrent devices, it is common to keep tabs on ground-electrode resistances to assure reliable operation.
Reliance upon earth return to operate low-voltage overcurrent devices is not reccommended and generally prohibited by consensus standards.
RE: Generation/ Low Resistance Grounding/ Distribution System
If you have multiple generators, each with its own grounding resistor, the total fault current will be the sum of all the generator neutral currents.
Of course, if this is an electric utility installation, you are not required to meet NEC, but I'd strongly recommend a grounding conductor be run with each set of phase conductors.
RE: Generation/ Low Resistance Grounding/ Distribution System
I have a plant that is serviced by a 5KV generation and distribution system. All of the loads on this system are three phase loads. If all of the generators are low resistance grounded, do I need to run a ground wire along with the phase wires from the 5KV switchgear to each of the 5KV loads (pad mounted gear, transformers, etc.)
///The low resistance system grounding (also known as medium resistance system grounding) is normally connected to the ground very close the generator neutral. A connection of equipment ground should be made between the low resistor and ground. This equipment ground is run to all conductive surfaces downstream to bring them all to the same equipotential level to avoid any hazardous conditions. The galvanized rigid conduit is normally considered sufficient for the ground return path. When the conduit distances become longer, e.g. hundreds of feet, it is prudent to add the grounding conductor and perform ground bonding in each pull box or junction box downstream.\\\
All of the loads in question will be grounded via "local" ground rods & loops.
///This is a good idea to reinforce the return path if the rigid steal conduit installation is in effect. However, it would not be covering certain fault, which relies on the conduit return path good resistance.\\\
If I do not run a ground wire with the phase conductors, is the earth an allowable return path for returning a phase to ground fault to the generator source?
///Theoretically, it could perform well; however, practically, the rigid steal conduits and ground conductors may provide lower ohmic return path.\\\
I have looked in the National Electrical Safety Handbook (NESC), IEEE Std. 142, NEC and Soares Book on Grounding to shed some light or guidance, but have come away with very little.
///There are good coverages in:
Donald Beeman "Industrial Power Systems Handbook," First Edition, McGraw-Hill Book Company, 1955,
Chapter 6 System Grounding
Chapter 7 Equipment Grounding\\\
RE: Generation/ Low Resistance Grounding/ Distribution System
RE: Generation/ Low Resistance Grounding/ Distribution System
But unless I'm reading it incorrectly, copper sheath is only allowable as grounding conductor for mineral-insulated (MI) cable. Armor can be used for AC and MC cable.
RE: Generation/ Low Resistance Grounding/ Distribution System
If I do not run a ground wire with the phase conductors, is the earth an allowable return path for returning a phase to ground fault to the generator source?
///It depends on its resistivity or impedance.\\\
RE: Generation/ Low Resistance Grounding/ Distribution System
RE: Generation/ Low Resistance Grounding/ Distribution System
See
http://okonite.com/engineering/shielding.html
RE: Generation/ Low Resistance Grounding/ Distribution System
"""For short lengths or where special bonding arrangements are used, grounding at one point only may be satisfactory."""
However, if there is a grounding conductor with the run, both sides of the cable shield are supposed to be grounded.
RE: Generation/ Low Resistance Grounding/ Distribution System